Field of the Invention
This disclosure relates generally to registration of sheets in a feed path and more particularly concerns a steering system for a sheet registration device in a high speed electrographic printing or copying machine.
In a typical electrophotographic printing or copying process, a photoconductive member is charged to a substantially uniform potential. The charged portion of the photoconductive member is exposed to a light image of an original document being reproduced. The charged photoconductive member is selectively discharged by exposure to the light in the irradiated areas. This creates an electrostatic latent image on the photoconductive member corresponding to the original document. This latent image on the photoconductive member is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules to the latent image forming a toner powder image on the photoconductive member. The toner powder image is then transferred from the photoconductive member to a copy sheet. The toner particles of the powder image are fixed permanently to the copy sheet with heat and pressure.
High quality documents in electrophotographic printers and copiers require registration of sheets of paper or other substrate to the photoreceptor for image transfer. Accurate registration control locates the image consistently with respect to the edge of the paper. Many machines use various types of sheet registration devices which sense the position of a sheet at a first location and generates a set of control signals to advance the sheet to arrive at a second location in proper registry and skew. These devices are dependent upon certain physical properties of the registration system being known. If, for example, drive rolls begin to wear, thus changing the diameter, it is possible that the sheet will not be registered in the proper position. It is desirable to have a system which can initially calibrate the sensors of a registration system and the associated drive mechanism and also to have a periodic update to account for wear and slippage and other physical properties which may degrade. A calibration system which will allow the use of inexpensive sensing devices is also desirable.
The following disclosures may relate to various aspects of the present embodiment:
U.S. Pat. No. 5,278,624 Patentee: Kamprath et al. Issue Date: Jan. 11, 1994
U.S. Pat. No. 5,715,514 Patentee: Williams et al. Issue Date: Feb. 3, 1998
Some portion of the foregoing disclosures may be briefly summarized as follows:
U.S. Pat. No. 5,278,624 describes a registration system for copy sheets using a pair of drive rolls and a drive system for commonly driving both drive rolls. A differential drive mechanism is provided for changing the relative angular position of one of the rolls with respect to the other roll to deskew the copy sheet. A control system is supplied with inputs representative of the skew of the copy sheet and controls the differential drive mechanism to deskew the copy sheet.
U.S. Pat. No. 5,715,514 describes a calibration system for a deskewing and registering device for an electrophotographic printing machine. The method includes a) moving a sheet from a first position to a second position along a paper path; b) sensing the position of the sheet at the first position and the second position; c) choosing a correction value to cause the sheet to change a lateral position from the first position to the second position; d) repeating the moving, sensing, and choosing steps until a predetermined adjustment is made when moving the sheet from the first position to the second position to determine a proper calibration value.
In accordance with one aspect of the present invention there is provided apparatus for calibrating a sheet registration device having independently, separately driven nips.
Pursuant to another aspect of the present embodiment, there is provided an apparatus for calibrating a sheet registering and deskewing device, comprising a plurality of sensors, located along a paper path, to sense a position of a sheet in the paper path at a first position and a second position, and to generate a signal indicative thereof, a pair of independently driven drive nips with steering mechanisms located in the paper path for forwarding the sheet from the first position to the second position and a controller, to receive signals from said plurality of sensors and to generate motor control drive signals for said pair of independently separately driven drive nips and steering mechanisms so as to induce a corrective action in the movement of the sheet from the first position to the second position in the paper path and to repeat the corrective action until a predetermined position is obtained.